This invention relates generally to electrostatographic reproduction machines, and particularly to a sheet stripping method and apparatus, and a fusing mechanism including same, for reliably stripping sheets from a fusing mechanism of a reproduction machine without sheet lead edge damage.
In a typical electrostatographic reproduction process machine, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is imagewise exposed in order to selectively dissipate charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated at a thermal fusing apparatus at a desired operating temperature so as to fuse and permanently affix the powder image to the copy sheet.
In order to fuse and fix the powder toner particles onto a copy sheet or support member permanently as above, it is necessary for the thermal fusing apparatus to elevate the temperature of the toner images to a point at which constituents of the toner particles coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the copy sheet or support member or otherwise upon the surface thereof. Thereafter, as the toner cools, solidification occurs causing the toner to be bonded firmly to the copy sheet or support member.
One approach to thermal fusing of toner images onto the supporting substrate is illustrated for example in U.S. Pat. Nos. 5,350,896, and 4,920,250. This approach involves passing the substrate with the unfused toner images thereon into nip contact between a pair of opposed fusing members, usually rollers but can be a roller and a belt, at least one of which is heated, and its temperature controlled at a desired high operating or fusing temperature level of about 350 degrees Fahrenheit. After such fusing, the substrate or sheet must then be stripped by a stripper from the heated fuser roller.
Conventional strippers typically come as individual fingers which tend to be flimsy or undesirably tear into and wear the fuser roll surface, or are designed with a uniform geometric shape across the width of the paper path. Unfortunately, it has been found that in an 80.degree. F. and 80% RH environment, a large number of dog eared copies are undesirably produced in high volume machines. Dog ears are defined as a severe deformation of the lead edge corner of a copy, but not necessarily folded over.
There is therefore a need for a sheet stripping method and apparatus, and a fusing mechanism including same, that can relaibly strip sheets from a fusing mechanism of a reproduction machine without sheet lead edge damage.